Magnetic resistance memory apparatus having multi levels and method of driving the same

ABSTRACT

A magnetic resistance memory apparatus capable of implementing various levels and a method of driving the same are provided. The magnetic resistance memory apparatus includes a first magnetic device that includes a fixed layer having a fixed magnetization direction, a tunnel layer disposed on the fixed layer, and a first free layer disposed on the tunnel layer having a variable magnetization direction, and a second magnetic device disposed on the first magnetic device including a plurality of free layers insulated with a spacer layer interposed.

CROSS-REFERENCES TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. 119(a) to Koreanapplication number 10-2011-0078268, filed on Aug. 5, 2011, in the KoreanPatent Office, which is incorporated by reference in its entirety as ifset forth in full.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a semiconductor integrated circuitdevice and a method of driving the same, and more particularly, to amagnetic memory apparatus having multi-levels and a method of drivingthe same.

2. Related Art

Along with high speed and low power consumption, a fast write/readoperation and a low operation voltage are also useful characteristics ofmemory devices embedded in the electronic appliances. Magnetic memoryapparatuses have been suggested to satisfy the useful characteristics.Magnetic memory apparatuses have high speed operation and/or nonvolatile characteristics.

In general, magnetic memory apparatuses may include magnetic tunneljunction patterns (hereinafter, referred to as MTJs). The MTJ mayinclude two magnetic materials and an insulating layer interposedbetween the two magnetic materials. A resistance of the MTJ is variedbased on magnetization directions of the two magnetic materials. Morespecifically, when the magnetization directions of the two magneticmaterials are anti-parallel to each other, the MTJ may have a largeresistance, and when the magnetization directions of two magneticmaterials are parallel to each other, the MTJ may have a smallresistance. Therefore, the MTJ may have different resistances, and it ispossible to read/write data according to a resistance difference.

Some magnetic random access memories (MRAM) have created an MTJ deviceby forming a ferromagnetic tunnel junction as a magnetoresistancedevice. The MTJ device includes three-layered layer including a magneticlayer, a nonmagnetic layer, and a magnetic layer and current flows totunnel the nonmagnetic layer (a tunnel barrier layer). Another MTJdevice design, called a spin valve structure, contains anantiferromagnetic layer that is disposed adjacent to a magnetic layer,and a magnetization direction is fixed to improve a sensibility of amagnetic field.

In the MRAM, a magnetization state of a ferromagnetic material forming aunit cell may be changed by a magnetic field. Alternatively, there arecurrent-induced magnetoresistance devices where a magnetization state ofa ferromagnetic material is changed by applying a current. Thecurrent-induced magnetoresistance devices are devices that control amagnetization direction by applying current to a magnetic layer tocontrol a magnetization direction of the magnetic layer.

A method of reading information from the current-inducedmagnetoresistance device is similar to a magnetic-induced MTJ or giantmagnetoresistance (GMR) devices. When a relative magnetization directionof a free magnetic layer and a fixed magnetic layer is parallel, thedevice has a low resistance. On the other hand, when a relativemagnetization direction of the free magnetic layer and a fixed magneticlayer is anti-parallel, the device has a high resistance. Therefore, theresistance states of the device may correspond to digital values “0” and“1”.

Currently, a dual GMR structure has been suggested to obtainmulti-levels other than “0” and “1” (J. Appl. Phys. 105, 103911, 2009).

As shown in FIG. 1, the dual GMR structure includes a first fixed layer10, a first spacer layer 20, a free layer 30, a second spacer layer 40,and a second fixed layer 50. The first and second fixed layers 10 and 50may include a ferromagnetic material having a fixed magnetism. The freelayer 30 may be an antiferromagnetic material having a magnetism thatvaries according to an external magnetic field. The first and secondspacer layers 20 and 40 may be formed of a CoFe/Cu/Co material.

When the magnetism of the first and second fixed layers 10 and 50 andthe free layer 30 are changed to implement multi-levels, the dual GMRcan implement only three levels, (0,0), (0,1) and (1,0), as shown inFIG. 2.

Therefore, a magnetic resistance memory apparatus capable ofimplementing more various levels is desired.

SUMMARY

The present invention provides a magnetic resistance memory apparatuscapable of implementing various levels and a method of driving the same.

According to an aspect of an exemplary embodiment, a magnetic resistancememory apparatus includes a first magnetic device that includes a fixedlayer having a fixed magnetization direction, a tunnel layer disposed onthe fixed layer, and a first free layer disposed on the tunnel layerhaving a variable magnetization direction, and a second magnetic devicedisposed on the first magnetic device including a plurality of freelayers insulated with a spacer layer interposed.

According to another aspect of an exemplary embodiment, a magneticresistance memory apparatus includes a first magnetic device thatincludes a first free layer having a variable magnetization direction, atunnel layer disposed on the first free layer, and a fixed layerdisposed on the tunnel layer and having a fixed magnetization directionand a second magnetic device disposed below the first magnetic deviceincluding a plurality of free layers insulated with a spacer layer beinginterposed. The fixed layer, the first free layer, and the plurality offree layers are configured to increase in coercive force toward thefixed layer.

According to still another aspect of an exemplary embodiment, a magneticresistance memory apparatus includes a fixed layer having a fixed firstmagnetization direction, a tunnel layer formed on the fixed layer, afirst free layer formed on the tunnel layer and having the firstmagnetization direction or a second magnetization directionanti-parallel to the first magnetization direction, a first spacer layerdisposed on the first free layer, a second free layer disposed on thefirst spacer layer and having the first magnetization direction or thesecond magnetization direction, a second spacer layer disposed on thesecond free layer, and a third free layer disposed on the second spacerlayer and having the first or second magnetization direction. The fixedlayer and the first through third free layers are formed to increase incoercive force that maintains the magnetization direction of the freelayers toward the fixed layer.

According to yet another aspect of an exemplary embodiment, a method ofdriving a magnetic resistance memory includes setting first throughthird free layers to have a second magnetization direction so that themagnetic memory apparatus has a first resistance level, changing themagnetization direction of a third free layer to the first magnetizationdirection by applying a first magnetic field so that the magnetic memoryapparatus has a second resistance level, changing the magnetizationdirection of a second free layer to the first magnetization direction byapplying a second magnetic field so that the magnetic memory apparatushas a third resistance level, and changing the magnetization directionof a first free layer to the first magnetization direction by applying athird magnetic field to have a fourth resistance level.

These and other features, aspects, and embodiments are described belowin the section entitled “DESCRIPTION OF EXEMPLARY EMBODIMENT”.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thesubject matter of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view illustrating a dual giant magnetoresistance (GMR) device in the related art;

FIG. 2 is a graph illustrating a resistance level for each magneticfield of a dual GMR in the related art;

FIG. 3 is a cross-sectional view illustrating a multi-layered magneticresistance memory apparatus according to an exemplary embodiment;

FIGS. 4A and 4B are cross-sectional views showing magnetizationdirections for each magnetic field of a multi-layered magneticresistance memory apparatus of FIG. 3, wherein FIG. 4A is a schematicdiagram illustrating a resistance variable mechanism where a fixed layerand free layers have the same in-plane magnetic anisotropy and FIG. 4Bis a schematic diagram illustrating a resistance variable mechanismwhere a fixed layer and free layers have the same out-of-plane magneticanisotropy;

FIG. 5 is a graph illustrating resistance levels for each magnetic fieldof the multi-layered magnetic resistance memory apparatus of FIG. 3; and

FIGS. 6 and 7 are cross-sectional views of multi-layered magneticresistance memory apparatuses according to other exemplary embodiments.

DESCRIPTION OF EXEMPLARY EMBODIMENT

Exemplary embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofexemplary embodiments (and intermediate structures). As such, variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,exemplary embodiments should not be construed as limited to theparticular shapes of regions illustrated herein but may be to includedeviations in shapes that result, for example, from manufacturing. Inthe drawings, lengths and sizes of layers and regions may be exaggeratedfor clarity. Like reference numerals in the drawings denote likeelements. It is also understood that when a layer is referred to asbeing “on” another layer or substrate, it can be directly on the otheror substrate, or intervening layers may also be present.

Referring to FIG. 3, the magnetic resistance memory apparatus accordingto an exemplary embodiment may include a first magnetic device 100 and asecond magnetic device 200 forming a stacking structure.

The first magnetic device 100 may be a magnetic tunnel junction (MTJ)that includes a fixed layer 110, a tunnel layer 120, and a first freelayer 130. The fixed layer 110 may be a ferromagnetic material layerwith a fixed magnetization direction. The tunnel layer 120 may be aninsulating layer that includes one or more of the following materials:magnesium oxide (MgO), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂),titanium oxide (TiO₂), yttrium oxide (Y₂O₃), and ytterbium oxide(Yb₂O₃). The first free layer 130 may be formed of a material with areversible magnetization direction in response to an applied magneticfield.

The second magnetic device 200 may be a GMR device that includes a firstspacer layer 210, a second free layer 220, a second spacer layer 230,and a third free layer 240 that are sequentially stacked. The GMR devicemay include a spin valve layer including a fixing magnetization layer, afree layer capable of changing a magnetization direction in response toan external magnetic field, and a spacer layer includes a nonmagneticconductive layer. In the exemplary embodiment, the GMR device is formedon the first magnetic device 100 so that the spin valve layer may be thefirst magnetic device 100.

The first and second spacer layers 210 and 230 may include of thenonmagnetic conductive material, for example, a material includes one ormore of the following materials: copper (Cu), cobalt iron (CoFe), andcobalt (Co). The first spacer layer 210 functions to insulate the firstmagnetic device 100 and the layers above the first spacer layer 210 inthe second magnetic device 200. The second spacer layer 230 functions toinsulate the second and third free layers 220 and 240. The second andthird free layers 220 and 240 are materials capable of reversingmagnetization directions in response to a magnetic field. In theexemplary embodiment, the third free layer 240 has a higher coerciveforce (Hc) than the second free layer 220, and the second free layer 220has a higher coercive force than the first free layer 130. Then, theresistance differences are between the fixed layer 110 and the firstfree layer 130, between the first free layer 130 and the second freelayer 220, between the second free layer 220 and the third free layer230, and between the third free layer 240 and the fixed layer 110.

A capping layer 300 may be further formed on the third free layer 240 toconnect with external devices. The capping layer 300 includes, forexample, a conductive layer such as Ti or tantalum (Ta).

Referring to FIGS. 4A and 5, in the magnetic resistance memoryapparatus, the fixed layer 110 and the first through third free layers130, 220, and 240 are formed so that the magnetization direction of thefixed layer is fixed in the direction of a first magnetizationdirection, and the first through third free layers 130, 220, and 240 mayhave a second magnetization direction anti-parallel to the firstmagnetization direction. In FIG. 5, an X-axis denotes a magnetic fieldand a Y-axis denotes a resistance. The first through third free layers130, 220, and 240 are formed to have the same second magnetizationdirection. Since the first through third free layers 130, 220, and 240have the same second magnetization direction, the first through thirdfree layers 130, 220, and 240 behave like a single magnetic layer. Thefixed layer 110 and the first through third free layers 130, 220, and240 have anti-parallel magnetization directions. The anti-parallelmagnetization directions of the fixed layer and the first through thirdfree layers 130, 220, and 240 means that the magnetic resistance memoryhas a first resistance state ({circle around (1)}).

When, for example, a first magnetic field (H1) that is sufficient isapplied to reverse the magnetization direction of the third free layer240, the magnetization direction of the third free layer 240 is changed.Since the coercive force of the third free layer 240 is the smallest,only the magnetization direction of the third free layer 240 is changed.Thereby, the magnetization direction of the third free layer 240 isreversed to match the first magnetization direction. When only themagnetic direction of the third free layer is parallel to the firstmagnetization direction, the magnetic resistance memory has a secondresistance state ({circle around (2)}) having a larger resistance thanthe first resistance state ({circle around (1)}).

Next, when, for example, a second magnetic field (H2) that is largerthan the first magnetic field (H1) that is sufficient is applied toreverse the magnetization direction of the second free layer 220, themagnetization direction of the second free layer 220 is changed. Themagnetization direction of the second free layer 220 and themagnetization direction of the third free layer 240 are changed to beparallel with the first magnetization direction. Therefore, the magneticresistance memory has a third resistance state ({circle around (3)}), astate that has a higher resistance level than the second resistancestate ({circle around (2)}).

Finally, when, for example, a third magnetic field (H3) larger than thesecond magnetic field (H2) that is sufficient is applied to reverse themagnetization direction of the first free layer 130, the magnetizationdirections of the first through third free layers 130, 220, and 240 arechanged to the first magnetization direction. When the first throughthird free layers 130, 220, and 240 all have the first magnetizationdirection, the magnetic resistance memory has a fourth resistance state({circle around (4)}). The fixed layer 110 and the first through thirdfree layers 130, 220, and 240 all have the same magnetization directionin the fourth resistance state ({circle around (4)}), so the fourthresistance state ({circle around (4)}) has the lowest resistance state.

As described above, the magnetic resistance memory apparatus in theexemplary embodiment can implement four different resistance levels bychanging a magnetic field. The four resistance levels can implement2-bit multi-levels.

FIG. 4A is a schematic diagram showing a magnetic resistance memoryapparatus where the fixed layer and the free layers have an in-planemagnetic anisotropy to a surface of the fixed layer, and FIG. 4B is aschematic diagram showing a magnetic resistance memory apparatus wherethe fixed layer and the free layers have an out-of-plane magneticanisotropy to a surface of the fixed layer.

FIG. 6 illustrates the case where a first magnetic device 100 forming anMTJ is stacked on a second magnetic device 200 forming a GMR device.Similar to the embodiment discussed above, the magnetic resistancememory apparatus can implement multi-levels by changing a magnetic fieldalthough the first magnetic device 100 is stacked on the second magneticdevice 200.

The present invention is not limited to the above-described exemplaryembodiments having two free layers 220 and 240 as the second magneticdevice. As shown in FIG. 7, three or more free layers 260 and 280 may befurther stacked with spacer layers 250 and 270 being interposed toforming a GMR device. In this case, a magnetic field is stepwisecontrolled in four or more steps to implement 2-bit levels or moremulti-bits levels.

As described above, a first magnetic device forming an MTJ and a secondmagnetic device forming a GMR device are stacked, and a magnetic fieldis stepwise applied to sequentially reverse a magnetization direction ofa free layer of the MTJ device and free layers of the GMR device,thereby implementing multi-levels. Since the MTJ device includes a fixedlayer and, for example, only the magnetization directions of the freelayers of the MTJ and GMR devices are reversed, multi-levels can beimplemented by a low critical current density (Jc). Further,multi-levels can be implemented by a single MTJ, thereby capable ofbeing applied in high integration devices.

While certain embodiments have been described above, it will beunderstood that the embodiments described are by way of example only.Accordingly, the devices and methods described herein should not belimited based on the described embodiments. Rather, the systems andmethods described herein should only be limited in light of the claimsthat follow when taken in conjunction with the above description andaccompanying drawings.

What is claimed is:
 1. A magnetic resistance memory apparatus,comprising: a first magnetic device that includes a fixed layer having afixed magnetization direction, a tunnel layer disposed on the fixedlayer, and a first free layer disposed on the tunnel layer having avariable magnetization direction; and a second magnetic device disposedon the first magnetic device, the second magnetic device including aplurality of spacer layers alternately stacked with a plurality of freelayers, wherein a lowest spacer layer, of the plurality of spacerlayers, is directly disposed on the first free layer.
 2. The magneticresistance memory apparatus of claim 1, wherein the fixed layer, thefirst free layer, and the plurality of free layers are configured toincrease in coercive force toward the fixed layer.
 3. The magneticresistance memory apparatus of claim 1, wherein the fixed layer, thefirst free layer, and the plurality of free layers have an in-planemagnetic anisotropy, respectively.
 4. The magnetic resistance memoryapparatus of claim 1, wherein the fixed layer, the first free layer, andthe plurality of free layers have an out-of-plane magnetic anisotropy,respectively.
 5. The magnetic resistance memory apparatus of claim 2,wherein the first free layer and the plurality of free layers arecapable of changing magnetization direction based on the presence of anapplied magnetic field of a sufficient coercive force.
 6. The magneticresistance memory apparatus of claim 1, wherein the tunnel layer is aninsulating layer.
 7. The magnetic resistance memory apparatus of claim1, wherein, the fixed layer includes a ferromagnetic material.
 8. Themagnetic resistance memory apparatus of claim 1, wherein, the firstmagnetic device forms a spin valve layer.
 9. The magnetic resistancememory apparatus of claim 1, wherein, the spacer layer includes anonmagnetic conductive material.